Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2002-01-03
2003-04-29
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S037000
Reexamination Certificate
active
06556457
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a method of controlling an inverter power generation apparatus having an inverter circuit to convert an output of an AC generator into an AC output of arbitrary frequency when it is operated in parallel to other power supply.
BACKGROUND OF THE INVENTION
An inverter power generation apparatus has been used for a power generation apparatus driven by an internal combustion engine as a primer.
In general, the inverter power generation apparatus comprises an AC generator driven by the internal combustion engine, a DC power supply section to convert an output voltage of the AC generator into a DC voltage, an inverter circuit to convert an output voltage of the DC power supply section into an AC output of predetermined frequency, a filter circuit to remove a harmonic component from an output of the inverter circuit, load connection terminals having an output of the filter circuit applied and a controller having PWM control means to control the inverter circuit in the form of pulse width modulation (referred to as PWM later) so as to output the AC voltage of predetermined waveform through the load connection terminals. In many cases, the controller is provided with overload protection means to stop the output of the inverter circuit when an overload current flows through the inverter circuit and the filter circuits in order to protect them.
The DC power supply section comprises a rectifier to rectify the output of the AC generator and a smoothing capacitor connected across the DC output terminals of the rectifier to generate a DC voltage across the smoothing capacitor.
The generally used inverter circuit comprises a bridge type switch circuit having a plural of switch arms connected in parallel to each other and each having an upper arm switch element and a lower arm switch element connected in series to each other. A pair of DC input terminals are led out of a common connection point of both ends of the switch arms while AC output terminals are led out of the connection point of the corresponding switch elements of each of the switch arms.
This inverter circuit has feedback diodes provided corresponding to the switch elements and connected in reverse parallel to the corresponding switch elements, respectively. Thus, A diode bridge full wave rectifier circuit is formed by the feedback diodes as viewed on the AC output terminals of the inverter circuit.
The PWM control means of the controller serves to output from the inverter circuit the AC voltage of intermittent waveform having a duty value “D” changing for every PWM cycle in accordance with an instant value of the AC output voltage applied through the load connection terminals to a load by carrying out the on-off operation of the pair of switch elements located at the diagonal position of the bridge of the inverter circuit at predetermined timing with a PWM signal of, pulse waveform applied to the pair of the switch elements.
The duty value “D” of the PWM control can be determined by multiplying a correction coefficient Kv by a reference duty value “Do” required for making a waveform of an AC output voltage to be output from the load connection terminals into predetermined waveform. In general, a ratio VA/VD of a rated value VA of the AC output voltage obtained across the load connection terminals to a DC power supply voltage VD is used for the correction coefficient Kv.
The AC voltage output from the inverter circuit is converted into an AC output voltage of smooth waveform having the harmonic component removed by the filter circuit.
The overload protection means provided in the controller controls the inverter circuit to stop the operation of the inverter when the load current equal to or more than the overload judgment current value flows through the load connection terminals whereby the switch elements of the inverter circuit is protected from the overload current.
With the inverter generator apparatus, since the DC voltage output from the DC power supply section is converted into the AC voltage of arbitrary frequency by controlling the inverter circuit, the AC voltage of predetermined frequency can be obtained from the load connection terminals in spite of what the revolution of the generator is. Also, the AC voltage of arbitrary magnitude can be obtained by controlling the duty value changing for every PWM cycle in the PWM control.
In case that the volume of the load is large, the aforementioned inverter power generation apparatus is sometimes required to be operated in parallel to the other AC power supply apparatus (referred to as an external AC power supply later). What is meant by “the external AC power supply” may be another inverter power generation apparatus formed in the same manner, an AC generator to generate an output voltage of frequency identical to that of the inverter power generation apparatus or a commercial AC power supply.
When the inverter power generation apparatus and the external AC power supply are operated in parallel to each other, the load connection terminals of both the inverter power generation apparatus and the external AC power supply are connected to each other and the electric power is simultaneously supplied from the inverter power generation apparatus and the external AC power supply to the load. In this case, the voltages generated by the inverter power generation apparatus and the external AC power supply are required to have a waveform, a crest value and a phase identical to each other.
Thus, in case that the inverter power generation apparatus and the external AC power supply are operated in parallel to each other, when the AC voltage is applied between the load connection terminals from the external power supply, the controller should control the inverter power generation apparatus so that the waveform, the crest value and the phase of the output voltage of the inverter power generation apparatus are coincident with those of the voltage applied from the external power supply
In the specification, it is premised that the external power supply having the output frequency equal to the output frequency of the inverter power generation apparatus is selected when they are operated in parallel to each other. In other words, it is premised that the output frequencies of the inverter power generation apparatus and the external AC power supply are coincident with each other.
The applicant has proposed an inverter power generation apparatus adapted to control an inverter circuit so that a waveform, a crest value and a phase of an AC output voltage applied across load connection terminals from the inverter circuit are coincident with those of an AC voltage applied from the external AC power supply from which the AC voltage is applied across the load connection terminals, which is disclosed in JP11-182294 and JP11-284277.
In the invention of JP11-182294, when an overcurrent flows through the inverter power generation apparatus, the output of the inverter power generation apparatus is once stopped and it is judged whether the overcurrent is caused by the overload or by the external AC power supply connected across the load connection terminals. When it is judged that the overcurrent is caused by the overload, the output of the inverter power generation apparatus is kept stopped and when it is judged that the overcurrent is caused by the voltage applied from the external AC power supply across the load connection terminals, the output of the inverter power generation apparatus is restored after the waveform, the crest value and the phase of the AC output voltage applied across the load connection terminals from the inverter circuit are made coincident with those of the AC voltage applied from the external AC power supply.
In the inverter power generation apparatus shown in JP11-284277, in case that the inverter circuit is controlled so as to output an AC output voltage of reference waveform from the inverter circuit through the load connection terminals, the difference between the phases of the reference waveform and the waveform of the actu
Nakagawa Masanori
Shimazaki Mitsuyoshi
Shinba Kaoru
Berhane Adolf Deneke
Kokusan Denki Co. Ltd.
Pearne & Gordon LLP
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